That led us to the article above, that seems to suggest that VMware quiescing, is now incompatible with Windows 2019.
The options are to disable it, or migrate to using legacy MBR disks.

This won't affect us too much, in our current environment - but if we need to introduce a Windows 2019 VM with a non-VSS aware DB (MySQL, Postgres etc) - what are the options? Just pre and post job scripts, rather than pre-freeze/post-thaw?

Well, you're not incorrect with that impression as VMware Tools quiescence provides similar pre-freeze and post-thaw scripts functionality. Just harder to use, as you have to deploy and update those scripts on every VM on your own somehow.

However, Veeam does not rely on VMware quiescence for anything at all.

And no, you don't lose anything at all: it's just a question of your script (for example, normally you should call flush as the last line of your custom pre-freeze script).